What is the best material for making gears?

[Sameh soliman]

Main Question or Discussion Point

For making gears as light and strong as possible, what is the best material to use?

 

[jedishrfu]

Probably nylon. I know choice of material is sometimes dictated by possible failure modes. At college, our physics machinist maintained the school clock tower.

He used a brass gear at one juncture realizing if the clock hands froze in winter then this gear would shear sparing a possible catastrophic binding of the whole clock mechanism.

 

[OmCheeto]

Probably nylon. ....

hmmm..... I'm not familiar with any cars with nylon transmission gears.

 

[CWatters]

They have other requirements such as low wear rates that the OP didn't mention.

 

[CWatters]

There are lots of different "nylons" some are reinforced with other materials. Some even contain lubricants.

 

[CWatters]

Advantages and disadvantages of plastic gears and some material references..

https://www.machinedesign.com/materials/plastic-gears-are-future

 

[russ_watters]

Since we are just guessing I'll add titanium while also saying that the constraint seems odd.

 

[jedishrfu]

hmmm..... I'm not familiar with any cars with nylon transmission gears.

Duh, how about model cars? :-)

Also, I didn't see where the OP mentioned cars in his/her post.

 

[Baluncore]

The biggest saving in weight is probably gained through using gears with several teeth in contact at the time, say an internal gear with a spur gear inside. Consider also Novikov or High-Conformal Gearing. That will also reduce the weight.

You could always cut smaller gears from a diamond with a laser.

 

[jedishrfu]

There's also magnetic gears:

https://en.wikipedia.org/wiki/Magnetic_gear

They have the advantage of minimal wear and will slip if the load is too great.

 

[Nugatory]

hmmm..... I'm not familiar with any cars with nylon transmission gears.

But nylon timing gears were once quite common, before the widespread adoption of timing chains.

Really, the "what is the best material for a gear?" question has no better answer than "It depends." All else being the same, stronger and lighter is better, but we also have to consider factors such as cost, expected lifetime, lubrication requirements, sound properties, acceptable backlash, ......

 

[OmCheeto]

But nylon timing gears were once quite common, before the widespread adoption of timing chains.

Really, the "what is the best material for a gear?" question has no better answer than "It depends." All else being the same, stronger and lighter is better, but we also have to consider factors such as cost, expected lifetime, lubrication requirements, sound properties, acceptable backlash, ......

And size.

Biggest gear I could find: 271 inch diameter [22.6 ft or 6.88 meters]
Smallest gear I could find: smaller than some horrible looking bug

For making gears as light and strong as possible, what is the best material to use?

Sameh, can you please let us know how big your gears are going to be. And perhaps, the torque requirements?
I've been looking for a reverse gear for a bicycle for several years, and as far as I can tell, no one makes one.
So I'm going to have to make one myself. So the answer to your question will probably help me also. Thanks!

ps. I don't recall seeing any bicycle gears made of nylon either. hmmm..... Guessing we're going to need to know if rocks and sticks and pant legs are going to be going through the gears. Ugh! Why does science have to be so complicated?

 

[CWatters]

Bike hub gears with reverse. Not used one.

https://www.sjscycles.co.uk/hubs-internal-hub-gear-brake/sturmey-archer-qsrc3-3spd-aluminium-quadricycle-hub-22t-36-hole/

Note it allows pedalling in reverse like a fixed wheel, not pedalling forwards and moving backwards.

 

[Baluncore]

But nylon timing gears were once quite common, before the widespread adoption of timing chains.

Unless Nylon or polymer gears are saturated with the right type of oil they will absorb water and other oil components which makes them swell by several percent during use.

Engines once used long trains of metal timing gears. They were heavy and noisy and would typically break teeth when an engine backfired. The capacitor in the magneto or distributor fails, so the timing gear train catastrophically consumes it's teeth.

Laminated composite gears made from fibre reinforced phenol polymers were used because they were lighter weight and were quieter, but the teeth wore down and the gear needed replacing. Laminated gears were substituted by light weight alloy gears that tended to bruise more quickly, or were brittle and fractured.

Steel timing chains were used but stretched as wear accumulated. Chains were noisy and heavy so they clatter when cold and fly out against the spring loaded tensioner blocks.

Stepped rubber belts were then used because they were light weight and quiet with longitudinal fibres to control stretch. But they have a limited life, so if you do not replace them, the engine loses phase and smashes the pistons against the valves, which today economically writes off the vehicle.

There is no one perfect solution to timing control in 4-stroke reciprocating engines.
Likewise, there is no perfect gear material or design. Lighter weight = less reliable = shorter life.

 

[russ_watters]

OP has not been back to clarify, so the thread is locked.